Light-modulated release of RFamide-like neuropeptides from nervus terminalis axon terminals in the retina of goldfish.
The nervus terminalis of teleosts, a cranial nerve anatomically associated with the olfactory system, projects to visual system targets including retina and optic tectum. It is known to contain gonadotropin-releasing hormone and RFamide-like peptides, but its function remains unknown. We have probed nervus terminalis function in goldfish by measuring peptide content in retina and tectum with a radioimmunoassay for A18Famide (neuropeptide AF; bovine morphine-modulating peptide). We found that retinal peptide content increased in the dark and decreased in the light, whereas tectal peptide content decreased in the dark and increased in the light. In addition, RFamide-like peptide content in the retina was transiently decreased by severing both olfactory tracts, increased in light-adapted eyes treated with a GABAergic agonist (isoguvacine), and decreased in dark-adapted eyes treated with GABAergic antagonists (bicuculline and picrotoxin). We also found that RFamide-like peptide release could be induced in dark-adapted isolated-superfused retinas by exposure to light or a high concentration (102.5 mM) of potassium ions. We interpret the increase and decrease in peptide content as reflecting a decrease and increase, respectively, in rate of peptide release. We propose that the release and accumulation of RFamide-like peptides in axon terminals of nervus terminalis processes in the retina are modulated primarily by neurons intrinsic to the retina and regulated by light. Peptide release appears to be inhibited tonically in the dark by GABA acting through GABAA receptors; light facilitates peptide release by disinhibition due to a reduction in GABA release. In addition, we propose that electrical signals originating outside the retina can override these intrinsic release-modulating influences.
Fischer
A J
AJ
Department of Anatomy, University of Calgary Faculty of Medicine, Alberta, Canada.
Stell
W K
WK
D000221:Adaptation, Ocular / Q000502:physiology; D000818:Animals; D001923:Brain Chemistry / Q000502:physiology; D002851:Chromatography, High Pressure Liquid; D003623:Dark Adaptation / Q000502:physiology; D006054:Goldfish / Q000378:metabolism*; D007150:Immunohistochemistry; D008027:Light; D009479:Neuropeptides / Q000378:metabolism*; D009833:Olfactory Pathways / Q000378:metabolism / Q000502:physiology; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000528:radiation effects; D011863:Radioimmunoassay; D012160:Retina / Q000378:metabolism* / Q000528:radiation effects
D009479:Neuropeptides; C058047:arginylphenylalaninamide